Flaps have long been used in gas turbine engine exhaust nozzle arrangements for selectively diverting portions of the hot engine exhaust gas flow stream. As engine exhaust gas temperatures have increased, it has been necessary to provide exhaust nozzle flaps which are resistant to the high temperature environment, yet lightweight and strong enough to prove functional in aircraft applications.
One method of providing such temperature resistance is to supply a flow of cooling gas, such as air, from the engine compressor or fan to the interior of the subject flaps to achieve the required cooling internally. Such air is typically supplied from a conduit or manifold in the static structure which is connected to the interior of the flap at the connecting joint between the movable flap and the nozzle static structure.
In certain two dimensional vectoring exhaust nozzle arrangements, it has been found advantageous to provide a convergent-divergent exhaust gas flow path to accommodate both augmented and unaugmented engine operation. One such 2-D convergent-divergent nozzle provides a forward convergent flap pivotally supported by the nozzle static structure, and an aftward divergent flap which is pivotally connected at its leading edge to the trailing edge of the convergent flap. In this particular arrangement, the divergent flap is positioned by means of a pair of drive links connected proximate the divergent flap trailing edge and selectively driven by linear actuators secured to the nozzle static structure.
As will be appreciated by those skilled in the art, the entire divergent flap in such an arrangement is freely movable with respect to the nozzle static structure and as a result does not have a support or other connection point through which a supply of cooling air may be delivered. As noted above, the presence of the divergent flap in the hot exhaust gas stream, and in particular during stream diverting orientations wherein the exhaust gas impinges directly on the flap surface, require some form of thermal protection to be provided. As also noted above, the most desirable form of thermal protection is an internal flow of cooling air which must be supplied to the divergent flap interior in sufficient quantity at all times during operation of the engine.